Fabrication of electrodes with multiple nanostructured thin catalytic layers

ABSTRACT

A method of making a reconstructed electrode having a plurality of nanostructured thin catalytic layers is provided. The method includes combining a donor decal comprising at least one nanostructured thin catalytic layer on a substrate with an acceptor decal comprising a porous substrate and at least one nanostructured thin catalytic layer. The donor decal and acceptor decal are bonded together using a temporary adhesive, and the donor substrate is removed. The temporary adhesive is then removed with appropriate solvents. Catalyst coated proton exchange membranes and catalyst coated diffusion media made from the reconstructed electrode decals having a plurality of nanostructured thin catalytic layers are also described.

RELATED CASES

This application is a Continuation-In-Part of U.S. application Ser. No.12/465,913 filed May 14, 2009, entitled ELECTRODE CONTAININGNANOSTRUCTURED THIN CATALYTIC LAYERS AND METHOD OF MAKING, which isincorporated herein by reference.

This application is related to U.S. application Ser. No. 12/718,306filed Mar. 5, 2010, entitled FABRICATION OF CATALYST COATED DIFFUSIONMEDIA LAYERS CONTAINING NANOSTRUCTURED THIN CATALYTIC LAYERS; and U.S.application Ser. No. 12/701,095, filed Feb. 5, 2010, entitledPREPARATION OF NANOSTRUCTURED THIN CATALYTIC LAYER-BASED ELECTRODE INK,which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to electrodes for fuel cells,and specifically to electrodes containing multiple nanostructured thincatalytic layers, and methods of making them.

BACKGROUND OF THE INVENTION

Electrochemical conversion cells, commonly referred to as fuel cells,produce electrical energy by processing reactants, for example, throughthe oxidation and reduction of hydrogen and oxygen. A typical polymerelectrolyte fuel cell comprises a polymer membrane (e.g., a protonexchange membrane (PEM)) with catalyst layers on both sides. Thecatalyst coated PEM is positioned between a pair of gas diffusion medialayers, and a cathode plate and an anode plate are placed outside thegas diffusion media layers. The components are compressed to form thefuel cell.

The currently widely used fuel cell electrocatalysts are platinumnanoparticles supported on carbon supports. Depending on the catalystsand loading, the electrodes prepared with carbon supported platinumcatalysts normally have thickness from several microns to about 10 or 20microns with porosities varying from 30% to 80%. One of thedisadvantages of these carbon supported catalysts is the poor corrosionresistance of carbon under certain fuel cell operating conditions, whichresults in fast performance degradation.

The catalyst layers can be made of nanostructured thin supportmaterials. The nanostructured thin support materials have particles orthin films of catalyst on them. The nanostructure thin catalytic layerscan be made using well known methods. One example of a method for makingnanostructured thin catalytic layers is described in U.S. Pat. Nos.4,812,352, 4,940,854, 5,039,561, 5,175,030, 5,238,729, 5,336,558,5,338,430, 5,674,592, 5,879,827, 5,879,828, 6,482,763, 6,770,337, and7,419,741, and U.S. Publication Nos. 2007/0059452, 2007/0059573,2007/0082256, 2007/0082814, 2008/0020261, 2008/0020923, 2008/0143061,and 2008/0145712, which are incorporated herein by reference. The basicprocess involves depositing a material on a substrate, such aspolyimide, and annealing the deposited material to form a layer ofnanostructured support elements, known as whiskers. One example of amaterial which can be used to form the nanostructured support elementsis “perylene red” (N,N′-di(3,5-xylyl)perylene-3,4,9,10bis(dicarboximide) (commercially available under the trade designation“C. I. PIGMENT RED 149” from American Hoechst Corp. of Somerset, N.J.)).A catalyst material is then deposited on the surface of nanostructuredsupport elements to form a nanostructured thin film (NSTF) catalystlayer, which is available from 3M.

The nanostructured thin catalytic layers can be transferred directly toa proton exchange membrane, such as a Nafion® membrane, using a hotpress lamination process, for example. The polyimide carrying substrateis then peeled off, leaving the layer of whiskers attached to themembrane, forming a catalyst coated membrane (CCM).

These types of nanostructured thin catalytic layers have demonstratedhigh catalytic activities, which is helpful to reduce the platinumutilization in fuel cell stacks. Most importantly, because thesupporting layer is not made of carbon as in the traditional platinumcatalysts for fuel cell application, the nanostructured thin catalyticlayers are more resistant to corrosion under certain fuel cell operatingconditions, and thus improve the fuel cell's durability.

However, after the annealing process is completed, a thin layer ofresidual non-crystallized perylene red remains at the surface of thepolyimide substrate. In addition, the deposition of catalyst materialcan form a thin film of catalyst material between the whiskers.Therefore, when the whiskers have been transferred to the PEM and thepolyimide substrate peeled off, the surface of the whiskers that wasadjacent to the polyimide substrate is exposed and becomes the surfaceof membrane electrode assembly (MEA). Consequently, the residualnon-crystallized perylene red backing, which originally was adjacent tothe polyimide substrate, and the thin catalyst film between the whiskersare exposed. This can be detrimental to the fuel cell operation becauseit can block water and gas transfer in and out of the electrode.

In addition, an MEA made with this type of whisker catalyst layer has anarrow range of operating conditions (i.e., they cannot be too dry ortoo wet) to provide good performance. If the fuel cell is operated underwet conditions, the thin layer of whiskers, which is less than 1 μmthick, cannot provide enough storage capacity for the product water,resulting in flooding. Under dry conditions, it is believed that not allportions of the whiskers are utilized to catalyze the reaction due topoor proton transfer characteristics.

Besides the NSTF whisker catalyst described above, there are otheruniformly dispersed (or dispersed with a desired pattern) catalyticnanostructured materials prepared on a substrate. For example, alignedcarbon nanotubes, aligned carbon nanofibers, or nanoparticles, and thelike could be grown on silicon or other substrates. Catalytic materialsare then deposited onto the nanostructured materials. Electrocatalystdecals incorporating such materials are described, for example, inHatanaka et al., PEFC Electrodes Based on Vertically Oriented CarbonNanotubes, 210^(th) ECS Meeting, Abstract #549 (2006); Sun et al.,Ultrafine Platinum Nanoparticles Uniformly Dispersed on Arrayed CN_(x)Nanotubes with High Electrochemical Activity, Chem. Mater. 2005, 17,3749-3753; Warren et al., Ordered Mesoporous Materials from MetalNanoparticle-Block Copolymer Self-Assembly, Science Vol. 320, 1748-1752(27 Jun. 2008).

The current distribution profile in the electrode varies at differentfuel cell operating conditions. (See e.g., “Cathode Catalyst Utilizationfor the ORR in a PEMFC Analytical Model and Experimental Validation,”Neyerlin et al., Journal of the Electrochemical Society, 154 (2)B279-B287 (2007)). The current is more concentrated on the cathodecatalyst close to the membrane due to poor proton conduction in theelectrode under dry operating conditions. The current is more uniformlydistributed across the cathode electrode thickness under humidifiedoperating conditions. Under very wet conditions, part of the cathodeelectrode would be flooded, and that part of the catalyst would notcontribute to the reaction. Controlling the catalyst distribution acrossthe cathode electrode thickness would help to provide an electrode thatperforms better under all conditions.

Depending on the fuel cell design, catalyst coated diffusion media(CCDM) sometimes has advantages over CCM. Gas diffusion media in PEMfuel cells are normally composed of a layer of carbon fiber paper orcarbon cloth and a microporous layer layer (MPL) thereon. The MPLnormally contains carbon powders and hydrophobic fluoropolymers. The MPLdoes not have strong inherent adhesive strength within itself and to thecarbon fiber substrate. Traditionally, CCDM is prepared by coating acatalyst containing ink directly on the gas diffusion layer, moreprecisely onto the MPL.

Therefore, there is a need for processing and constructing catalystcoated diffusion media which can provide good performance over a widerrange of operating conditions.

SUMMARY OF THE INVENTION

This invention provides a method of making reconstructed electrodedecals having a plurality of nanostructured thin catalytic layers. Oneor more donor decals having at least one nanostructured thin catalyticlayer is combined with an acceptor decal having at least onenanostructured thin catalytic layer using an adhesive. The donor decaland acceptor decals are bonded together, and the donor decal substrateis removed. The adhesive is then removed with appropriate solvents. Thetwo or more nanostructured thin catalytic layers on the acceptor decalsubstrate can be further processed, if desired. Such further processingincludes, but is not limited to, incorporating additionallayers/materials to construct an improved electrode (e.g., to increasethe water storage capacity, or to increase conductivity). Thereconstructed electrode decal with the plurality of nanostructured thincatalytic layers can be combined with proton exchange membranes(catalyst coated membrane (CCM)) or diffusion media (catalyst coateddiffusion media (CCDM)) and used to fabricate the membrane electrodeassembly (MEA) for use in fuel cell stack.

In one embodiment of the present invention, a method of making areconstructed electrode decal having a plurality of nanostructured thincatalytic layers is provided. The method includes providing a firstdonor decal comprising a substrate with a nanostructured thin catalyticlayer; providing an acceptor decal comprising a porous substrate with ananostructured thin catalytic layer; applying an adhesive adjacent tothe nanostructured thin catalytic layer of the first donor decal, or thenanostructured thin catalytic layer of the acceptor decal, or both;bonding the nanostructured thin catalytic layer of the first donor decaladjacent to the nanostructured layer of the acceptor decal with theadhesive; removing the donor substrate; and removing the adhesive toform the reconstructed electrode decal comprising the porous acceptorsubstrate, the acceptor nanostructured thin catalytic layer adjacent tothe porous acceptor substrate, and the first donor nanostructured thincatalytic layer adjacent to the acceptor nanostructured thin catalyticlayer on a side opposite the porous acceptor substrate.

In another embodiment of the present invention, a reconstructedelectrode decal having a plurality of nanostructured thin catalyticlayers is provided. The reconstructed electrode decal comprises a poroussubstrate; a first transferred nanostructured thin catalytic layeradjacent to the porous transfer substrate; and a second transferrednanostructured thin catalytic layer adjacent to the first transferrednanostructured thin catalytic layer on a side opposite the poroussubstrate.

In another embodiment, a catalyst coated proton exchange membrane isprovided. The catalyst coated proton exchange membrane comprises: aproton exchange membrane; a first transferred nanostructured thincatalytic layer adjacent to the proton exchange membrane; and a secondtransferred nanostructured thin catalytic layer adjacent to the firsttransferred nanostructured thin catalytic layer on a side opposite theproton exchange membrane.

In another embodiment, a catalyst coated diffusion media is provided.The catalyst coated diffusion media comprises: a diffusion mediacomprising a gas diffusion media layer with an adjacent microporouslayer; a first transferred nanostructured thin catalytic layer adjacentto the microporous layer; and an second transferred nanostructured thincatalytic layer adjacent to the first transferred nanostructured thincatalytic layer on a side opposite the microporous layer.

By adjacent, we mean next to, but not necessarily directly next to.There can be one or more intervening layers, as discussed below.

By first transferred nanostructured thin catalytic layer and secondtransferred nanostructured thin catalytic layer, we mean that there aretwo nanostructured thin catalytic layer which have been transferred tothe porous substrate, the proton exchange member, or the diffusionmedia. The transferred nanostructured thin catalytic layers areindividual layers that have been transferred separately from onestructure to another at different times. For example, the firsttransferred nanostructured thin catalytic layer could have beentransferred to an acceptor substrate and the second nanostructured thincatalytic layer could have been transferred from a donor decal to theacceptor decal. The first and second nanostructured thin catalyticlayers could then be transferred to the proton exchange or diffusionmedia. Other transfer sequences are also possible. The terms first andsecond do not imply any order of transfer, but are used to distinguishthe two nanostructured thin catalytic layers. The terms do not includemultiple nanostructured thin catalytic layers that are grown one on topof the other and then transferred together to another structure.However, such multiple nanostructured thin catalytic layers that aregrown one on top of the other could be used as a first or secondnanostructured thin catalytic layer.

Other features and advantages of the present invention will be apparentin light of the description of the invention embodied herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of specific embodiments of thepresent invention can be best understood when read in conjunction withthe following drawings, where like structure is indicated with likereference numerals, where various components of the drawings are notnecessarily illustrated to scale, and in which:

FIGS. 1A-D are an illustration of one embodiment of general method offabricating a nanostructured thin catalytic layer electrode donor decalaccording to one or more embodiments;

FIGS. 2A-D are an illustration of one embodiment of a general method offabricating a nanostructured thin catalytic layer electrode acceptordecal according to one or more embodiments;

FIGS. 3A-C are an illustration of one embodiment of a general method offabricating a reconstructed electrode decal having a plurality ofnanostructured thin catalytic layers;

FIGS. 4A-C are an illustration of another embodiment of general methodof fabricating a nanostructured thin catalytic layer electrode donordecal according to one or more embodiments;

FIGS. 5A-C are an illustration of another embodiment of a general methodof fabricating a nanostructured thin catalytic layer electrode acceptordecal according to one or more embodiments;

FIGS. 6A-H are an illustration of one embodiment of a method offabricating a reconstructed electrode decal having three nanostructurethin catalytic layers;

FIGS. 7A-D are an illustration of one embodiment of a method offabricating a reconstructed electrode decal having one nanostructurethin catalyst layer for CCM fabrication;

FIGS. 8A-B are SEM cross-section images of the reconstructed electrodedonor decal of FIG. 1C;

FIGS. 9A-D show top down SEM images of a nanostructured thin catalyticlayer on the porous transfer substrate at the stage of FIG. 1D atdifferent magnifications;

FIGS. 10A-B show SEM images of the cross-section of the nanostructuredthin catalytic layer on the porous transfer substrate of FIG. 9;

FIGS. 11A-B are SEM images of the reconstructed electrode donor decal ofFIG. 7D;

FIGS. 12A-B show SEM images of the cross-section of one embodiment of acatalyst coated membrane made with the reconstructed nanostructured thincatalytic layer electrode decal of FIG. 11;

FIGS. 13A-D are an illustration of another embodiment of the method offabricating an electrode decal containing a nanostructured thincatalytic layer;

FIGS. 14A-B show SEM images of the cross-section of one embodiment of ananostructured thin catalytic layer on the porous transfer substrate ofFIG. 13D;

FIGS. 15A-B show SEM images of the cross-section of one embodiment of acatalyst coated membrane made with the reconstructed nanostructured thincatalytic layer electrode decal of FIG. 14;

FIGS. 16A-D are an illustration of another embodiment of the method offabricating an electrode decal containing a nanostructured thincatalytic layer;

FIGS. 17A-B are SEM images of the cross-section of one embodiment of ananostructured thin catalytic layer on the porous substrate of FIG. 16D;

FIGS. 18A-B show SEM images of the cross-section of one embodiment of acatalyst coated membrane made with the reconstructed nanostructured thincatalytic layer electrode decal of FIG. 17;

FIGS. 19A-D are an illustration of another embodiment of the method offabricating an electrode decal containing a nanostructured thincatalytic layer;

FIGS. 20A-B are SEM images of the cross-sections of embodiments ofnanostructured thin catalytic layer on the porous transfer substratemade using the method of FIG. 19;

FIGS. 21A-B are SEM images of the cross-sections of embodiments ofcatalyst coated membrane made with porous nanostructured thin catalyticlayer electrode decals of FIG. 20;

FIGS. 22A-D are an illustration of one embodiment of a method offabricating a reconstructed electrode decal having two nanostructuredthin catalytic layers;

FIGS. 23A-B are SEM images of the cross-sections of embodiments of thenanostructured thin catalytic layers on the porous transfer substratemade using the method of FIG. 22;

FIGS. 24A-B are SEM images of the cross-sections of embodiments ofcatalyst coated membrane made with porous nanostructured thin catalyticlayer electrode decals of FIG. 23;

FIGS. 25A-B are an illustration of one embodiment of general method ofpretreating diffusion media for fabricating a CCDM having ananostructured thin catalytic layer electrode according to one or moreembodiments;

FIGS. 26A-D are an illustration of one embodiment of a general method oftransferring a nanostructured thin catalytic layer electrode to thepretreated diffusion media of FIG. 25 and adding additional layersthereon according to one or more embodiments;

FIGS. 27A-E are an illustration of one embodiment of fabricating acatalyst coated diffusion media made with a nanostructured thincatalytic layer using method of FIG. 25 and FIG. 26 according to one ormore embodiments;

FIGS. 28A-B are SEM images of the cross-sections of embodiments of thecatalyst coated diffusion media of FIG. 27;

FIGS. 29A-B are SEM images of the cross-sections of the MEA made usingthe catalyst coated diffusion media of FIG. 28;

FIGS. 30A-B are SEM images of the cross-sections of embodiments of thecatalyst coated diffusion media having a nanostructured thin catalyticlayer and an additional catalyst layer coating according to method inFIG. 27;

FIGS. 31A-B are SEM images of the cross-sections of MEAs made using thecatalyst coated diffusion media of FIG. 30;

FIGS. 32A-D are an illustration of one embodiment of a general method offabricating a catalyst coated diffusion media made with twonanostructured thin catalytic layers;

FIG. 33 is an SEM image of the cross-section of an embodiment of thereconstructed electrode decal containing two nano structured thincatalyst layers using the donor decal of FIG. 1 and the alternativeacceptor decal of FIG. 5;

FIG. 34 is a graph showing the fuel cell performance of a prior artmembrane electrode assembly by directly transferring the nanostructuredthin catalytic layer (0.15 mg Pt/cm²) to the PEM from the carryingsubstrate at various temperatures;

FIG. 35 is a graph showing the fuel cell performance of a prior artmembrane electrode assembly by directly transferring the nanostructuredthin catalytic layer (0.05 mg Pt/cm²) to the PEM from the carryingsubstrate at various temperatures;

FIG. 36 is a graph showing the fuel cell performance of a catalystcoated membrane based membrane electrode assembly shown in FIG. 12,containing one nanostructured thin catalytic layer (0.05 mg Pt/cm²) atvarious temperatures;

FIG. 37 is a graph showing the fuel cell performance of a catalystcoated membrane based membrane electrode assembly shown in FIG. 18,containing a nanostructured thin catalytic layer (0.05 mg Pt/cm²) and alayer of Pt/C catalyst (0.05 mg Pt/cm²) at various temperatures;

FIG. 38 is a graph showing the fuel cell performance of a catalystcoated membrane based membrane electrode assembly shown in FIG. 24,containing the two nanostructured thin catalytic layers and (2×0.05 mgPt/cm²) and a layer of Pt/C catalyst (0.05 mg Pt/cm²) at varioustemperatures;

FIG. 39 is a graph showing the comparison of the fuel cell performanceof catalyst coated membrane based membrane electrode assemblies shown inFIG. 12, FIG. 18, and FIG. 24, and the two prior art MEAs (at 0.05 mgPt/cm² and 0.15 mg Pt/cm² loading) under a dry testing condition;

FIG. 40 is a graph showing the comparison of the fuel cell performanceof catalyst coated membrane based membrane electrode assemblies shown inFIG. 12, FIG. 18, and FIG. 24, and the two prior art MEAs (at 0.05 mgPt/cm² and 0.15 mg Pt/cm² loading) under a wet testing condition;

FIG. 41 is a graph showing the fuel cell performance of a catalystcoated diffusion media based membrane electrode assembly shown in FIG.29, at various temperatures;

FIG. 42 is a graph showing the fuel cell performance of a catalystcoated diffusion media based membrane electrode assembly shown in FIG.31, at various temperatures.

DETAILED DESCRIPTION

Methods of transferring a nanostructured thin catalytic layer from thecarrying substrate to a porous transfer substrate coated with anadhesive are described in U.S. Ser. No. 12/465,913, filed May 14, 2009,entitled Electrode Containing Nanostructured Thin Catalytic Layers AndMethod Of Making, which is incorporated herein by reference. Thenanostructured thin catalytic layer can be further processed on theporous transfer substrate. The adhesive can be removed, and any residualmaterial (e.g., non-crystallized perylene red used to make whiskers, orcatalysts used to make carbon nanotubes, and the like) can also beremoved. Additional layers can be incorporated into the structure toincrease the water storage capacity, if desired. Ionic conductingcomponents can be incorporated into the nanostructured thin catalyticmatrix, if desired. An electrode incorporating such a nano structuredthin catalytic layer provides good performance over a wider range ofoperating conditions, and takes advantage of its high catalytic activityand resistance to corrosion under certain fuel cell operatingconditions.

The processes generally involve methods of transferring thenanostructured thin catalytic layer from its carrying substrate toanother substrate. The carrying substrate can be the substrate thenanostructured thin catalytic layer was grown on or carried on. Thetransfer substrate that the nanostructured thin catalytic layer will betransferred to is pre-coated with a thin layer of temporary adhesiveand/or a layer that contains particles (e.g., conductive particles,including but not limited to, carbon powder, and carbon fibers;catalyst; titanium dioxide; silica; nanofibers; nanotubes; orcombinations thereof), and/or ionomer, and the temporary adhesive. Indoing so, the catalyst loading (mg/cm²) on the transfer substrate isessentially the same as the carrying substrate where the nanostructuredthin catalytic layer was formed.

An ionomer solution or an ink that contains particles and ionomer can bedeposited on top of the nanostructured thin catalytic layer to formadditional layers, if desired. An electrode with a nanostructured thincatalytic layer and additional layers and components can thus beprepared for later MEA or CCM fabrication.

Because of the transfer of the nanostructured thin catalytic layer fromthe carrying substrate to the transfer substrate, the nanostructuredthin catalytic layer is inverted on the transfer substrate compared tothe carrying substrate. In other words, after the transfer, the surfaceof the nanostructured thin catalytic layer that was exposed on thecarrying substrate is adjacent to the transfer substrate, while thesurface that was adjacent to the carrying substrate is exposed. Thesurface that was adjacent to the carrying substrate can contain residualmaterials that were used to form the nanostructured catalyst supportelements (e.g., residual non-crystallized perylene red, or catalyststhat were used to grow carbon nanofibers or carbon nanotubes, and thelike), which can be cleaned through later treatment. This surface mayalso have a film of fuel cell catalyst material.

One method of transferring a nanostructured thin catalytic layer from acarrying substrate to a porous transfer substrate involves providing anelectrocatalyst decal comprising a carrying substrate having thenanostructured thin catalytic layer thereon, the nanostructured thincatalytic layer having a first surface and a second surface, the firstsurface of the nanostructured thin catalytic layer adjacent to thecarrying substrate; providing a porous transfer substrate with anadjacent adhesive layer; adhering the second surface of thenanostructured thin catalytic layer to the adhesive layer to form acomposite structure; removing the carrying substrate from the compositestructure; and removing the adhesive layer from the composite structureto form a reconstructed electrode decal comprising the porous transfersubstrate and the nanostructured thin catalytic layer, wherein thesecond surface of the nanostructured thin catalytic layer is adjacent tothe porous transfer substrate.

The porous transfer substrate can optionally have an intermediate layerfirst coated on the transfer layer before the adhesive is coatedthereon. The intermediate layer can be positioned between the transfersubstrate and the adhesive layer. It can include one or more ofadhesive; ionomer; conductive particles, including but not limited to,carbon powder, and carbon fiber; catalyst; titanium dioxide; silica;nanofibers; nanotubes; or combinations thereof. For example, an ionomercan be added to increase the proton conduction of the whisker catalystsunder dry conditions. A hydrophobic component, such as PTFE particles,can be included to improve wet performance.

Conductive particles, such as carbon (powder, fibers, or both), orcatalyst (typically the catalyst would be on a carbon support) can beincluded to increase the overall electrode thickness and thus improvethe product water storage capability.

More durable conductive particles can also be used to provide void spacewithin the electrode for product water storage. Suitable compoundsinclude, but are not limited to, conductive borides, carbides, nitrides,and silicides (B, C, N, Si). Suitable metals for the conductiveparticles include, but are not limited to Co, Cr, Mo, Ni, Ti, W, V, Zr.The use of such compounds, for example, TiN, is described in USPublication 2006/251954. One advantage of nanostructured thin catalyticlayers over carbon supported electrodes is durability enhancementbecause the carbon support is susceptible to corrosion especially duringfuel cell startup. These other conductive materials have not been fullysuitable for electrode supports because they do not provide enoughsurface area, and consequently, Pt dispersion, as is obtainable withcarbon. However, for the present use, the conductive particles wouldonly need to function to provide void space and conductivity but notcatalyst support, so the high surface area is not needed. Materialdurability is needed in the acidic and high electrochemical potentialfuel cell environment. Thus, their use would be acceptable.

Titanium dioxide and/or silica, which are hydrophilic and could be usedto retain product water under dry conditions, can also be included. Theaddition of non-conductive particles such as titanium dioxide or silicawould likely require the addition of a conductive material to providethe electrical conductivity function. Ionomer could also be added tothis layer or be pulled in by later coating processes to provide theneeded protonic conductivity for this layer.

Nanofibers and/or nanotubes, which can be used as structural materialsto incorporate into the intermediate layer, can also be used.

When the intermediate layer includes adhesive, the method furtherincludes removing the adhesive in the intermediate layer after thecarrying substrate is removed.

A solution can optionally be coated onto the nanostructured thincatalytic layer after the carrying substrate and the adhesive layer havebeen removed, the solution forming an additional layer on the firstsurface of the nanostructured thin catalytic layer. The solution caninclude, but is not limited to, one or more of, an ionomer; conductiveparticles, including, but not limited to carbon powder, and carbonfibers; catalyst; titanium dioxide; silica; nanofibers; nanotubes; orcombinations thereof.

The reconstructed electrode decal can be used to make a catalyst coatedmembrane. The method comprises providing an electrocatalyst decalcomprising a carrying substrate having a nanostructured thin catalyticlayer thereon, the nanostructured thin catalytic layer having a firstsurface and a second surface, the first surface of the nanostructuredthin catalytic layer adjacent to the carrying substrate; providing aporous transfer substrate with an adjacent adhesive layer; adhering thesecond surface of the nanostructured thin catalytic layer to theadhesive layer to form a composite structure; removing the carryingsubstrate from the composite structure; and removing the adhesive layerfrom the composite structure to form an electrode decal comprising theporous transfer substrate and the nanostructured thin catalytic layer,wherein the second surface of the nanostructured thin catalytic layer isadjacent to the porous transfer substrate; providing a proton exchangemembrane; transferring the nanostructured thin catalytic layer from theelectrode decal to a first surface of the proton exchange membrane toform a catalyst coated membrane, the first surface of the nanostructuredthin catalytic layer being adjacent to the first surface of the protonexchange membrane.

The reconstructed electrode decal comprises a porous transfer substrate;and a nanostructured thin catalytic layer having a first surface and asecond surface, the nanostructured thin catalytic layer having beentransferred from a carrying substrate, the first surface having beenadjacent to the carrying substrate, and wherein the second surface ofthe nanostructured thin catalytic layer is adjacent to the poroustransfer substrate.

The catalyst coated proton exchange membrane comprises a proton exchangemembrane; a nanostructured thin catalytic layer having a first surfaceand a second surface, the nanostructured thin catalytic layer havingbeen transferred from a carrying substrate to a transfer substrate, thefirst surface having been adjacent to the carrying substrate, the secondsurface having been adjacent to the transfer substrate, and wherein thefirst surface is adjacent to the proton exchange membrane.

This process transfers the nanostructured thin catalytic layers from thecarrying substrate they are grown on or carried on to another transfersubstrate. In doing so, the nanostructured thin catalytic layer isinverted so that the surface that was adjacent to the carrying substrateis exposed. This allows that surface to be cleaned, and the residualmaterial (if present) to be removed, which can help improve electrodeperformance and durability. This also places any platinum films thatwere adjacent to the carrying substrate towards the membrane where sucha film would not impede gas mass transfer (as it would be if it werelocated towards the DM side of the electrode).

The transfer process allows additional layers to be deposited on thecleaned surface of the nanostructured thin catalytic layer aftertransfer. Additional layers can also be pre-coated on the poroustransfer substrate before the adhesive layer is coated on. Thepre-coated layer can contain particles (e.g., conductive particlesincluding, but not limited to, carbon powder, and carbon fibers;catalyst; titanium dioxide; silica; nanofibers; nanotubes; orcombinations thereof), and/or ionomer, and the temporary adhesive aswell. As a result, the structures of the electrodes formed and thecatalyst coated membranes made using them can be adjusted by selectionof the location, types, composition, and thicknesses of these additionallayers.

The reconstructed electrodes on the porous transfer substrate formed bythe above process can then be used to form a catalyst coated membrane.The reconstructed electrode is adhered to one or both surfaces of a PEM,and the porous transfer substrate is then removed to form the catalystcoated membrane. Typically, pressure and optionally heat are applied toadhere the reconstructed electrodes containing the nanostructured thincatalytic layer to the PEM, allowing transfer of the reconstructedelectrode from the transfer substrate to the PEM. Processes suitable foradhering the reconstructed electrodes containing the nanostructured thincatalytic layer to the PEM include, but are not limited to, staticpressing with heat and pressure, or for continuous roll production,laminating, nip rolling, or calendering.

Generally, a pressure of between about 90 and about 900 MPa can be usedto adhere the reconstructed electrodes containing the nanostructuredthin catalytic layers to the PEM. The press temperature should be highenough to attach the reconstructed electrodes containing thenanostructured thin catalytic layers to the PEM, but below the meltingtemperature of the PEM. For example, the press temperature is generallybetween about 80° and about 300° C. The pressing time is typicallygreater than about 1 second; for example, a pressing time of about oneminute is suitable for many situations.

When the MEA or CCM fabrication process using one nanostructured thincatalytic layer is done and the transfer substrate is removed, thesurface which was exposed on the original nanostructured thin catalystlayer carrying substrate will be again exposed to be the surface of theCCM. In general, the surface exposed on the original carrying substrateis more open compared to the surface against the carrying substrate. Sothe CCM prepared through the process described above would be morefavorable for reactant gas transport and product water removal when asingle nanostructured thin catalytic layer is used.

The catalyst coated membrane can be used in a membrane electrodeassembly for a fuel cell, or other electrochemical energy conversiondevices, such as electrolyzers.

Additional nanostructured thin catalytic layers can be added to therestructured electrode decal, if desired. The reconstructed electrodedecals having a plurality of nanostructured thin catalytic layer canoptionally include one or more intermediate layers which can be designedto increase water storage capacity and/or improve conductivity, ifdesired. The intermediate layers can be between the substrate and thenanostructured thin catalytic layer, between the nanostructured thincatalytic layers, or on top of the upper nanostructured thin catalyticlayer.

By using more than one nanostructured thin catalytic layer, structurescan be designed and fabricated to have increased overall electrode waterstorage capacity. The catalyst loading in each of the nanostructuredthin catalytic layers can be adjusted. In addition, the intermediatelayers can use different types and/or amounts of additional material atdifferent positions in the structure; for example, a more porous carbonlayer can be used closer to the diffusion media. Furthermore, ionomercan be included in one or more intermediate layers, and an ionomergradient can be built into the structure with the highest ionomerconcentration near the proton exchange membrane.

Such adjustments will allow an electrode to be designed to performoptimally under both dry and wet conditions. Under dry conditions, mostof the current will be drawn from the nanostructured thin catalyticlayer(s) close to the membrane, while under wet conditions, most of thecurrent will be drawn from nanostructured thin catalytic layers furtherfrom the membrane.

The basic process is modified to make reconstructed electrode decalshaving more than one nanostructured thin catalytic layers, as describedbelow.

Reconstructed electrode decals having a plurality of nanostructured thincatalytic layers can be made by combining one or more “donor” decalswith an “acceptor” decal.

A reconstructed electrode decal with a single nanostructured thincatalytic layer as described above can used as a donor decal. Donordecals can be made as shown in FIG. 1. FIG. 1A shows a transfersubstrate 105 coated with an adhesive layer 110. The transfer substrate105 can be any stiff or soft porous substrate. If the nanostructuredthin catalytic layer is made on a smooth substrate, a stiffer substratecan be used as the transfer substrate. Stiff substrates can also be usedif a thick layer of the temporary adhesive is coated on the transfersubstrate, and the thickness of the adhesive layer is thicker than theroughness feature (e.g., corrugations) of the carrying substrate. Forexample, if the carrying substrate has a surface feature (e.g.,corrugations) which is 6 microns between the highest and lowest pointsof the corrugated structure, then the thickness of the adhesive layershould be greater than 6 microns.

The transfer substrate can be porous or non-porous.

Porous transfer substrates are desirable because pores of the poroustransfer substrate can then act as a drain for waste products used infurther processing the nanostructured thin catalytic layer. It alsoallows vacuum to be applied to help hold the nanostructured thincatalytic layer in place after the adhesive is removed. Soft poroussubstrates can accommodate the surface roughness of the carryingsubstrate in case the nanostructured thin catalytic layers were not madeon smooth substrates. Suitable types of porous substrates include, butnot are limited to, porous polyethylene (PE), porous polypropylene (PP),porous polyester, porous Nylon, polyimide (PI), expandedpolytetrafluoroethylene (ePTFE), and porous siloxane.

One suitable porous substrate is expanded polytetrafluoroethylene(ePTFE). ePTFE is soft, which allows it to receive the nanostructuredthin catalytic layers from both the top and the bottom of thecorrugations of the electrocatalyst decal on which they were grown.ePTFE has another advantage when an adhesive dissolved in a hydrophilicsolution is used. Because ePTFE is hydrophobic, only a thin film of theadhesive, such as polyvinyl alcohol (PVA), is formed on the surface ofthe ePTFE when the adhesive is coated from a PVA water solution, and thePVA will not fill the pores of the ePTFE substrate.

The adhesive layer 110 acts as a temporary glue which adheres thenanostructured thin catalytic layer and the porous substrate together,allowing the removal of the nanostructured thin catalytic layer from thecarrying substrate. Any suitable adhesive can be used. Desirably, theadhesive is easily removable, and does not poison the catalyst. Watersoluble adhesives are desirable because they can be easily removed withwater. However, other solvents can be used to remove the adhesive, ifdesired. Suitable adhesives include, but are not limited to, polyvinylalcohol (PVA), polyethylene oxide, polyacrylate, polyethylene vinylacetate, and soluble cellulose. One suitable adhesive is a water solublePVA, for example, a water soluble PVA having a molecular weight (MW) ofabout 10,000. Generally, the PVA layer loading is between about 0.1mg/cm² and about 10 mg/cm², or about 0.5 mg/cm² to about 2 mg/cm².

The adhesive layer can optionally include one or more additionalmaterials, including, but not limited to, ionomer, conductive particles,including, but not limited to, carbon powder, and carbon fibers;catalyst; titanium dioxide; silica; nanofibers; or nanotubes, ifdesired. If the adhesive layer contains one or more additionalmaterials, there should be sufficient adhesive in the layer so that thenanostructured thin catalytic layer will adhere to it. If ionomer isincluded, the amount of ionomer should be enough so that, combined withthe adhesive, it will hold the nanostructured thin catalytic layer, butnot so much that it blocks the pores of the porous transfer substrate.The adhesive layer desirably includes an adhesive, such as PVA, andionomer.

The porous transfer substrate can be either hydrophobic or hydrophilic.Preferably, an adhesive soluble in an aqueous or hydrophilic solution isapplied when the porous transfer substrate is hydrophobic, or viceversa. This allows a thin film of the adhesive to form only on thesurface of the porous transfer substrate. In this way, the pores are notfilled with the adhesive initially.

As shown in FIG. 1B, an electrocatalyst decal is provided. Theelectrocatalyst decal includes a carrying substrate 115 withnanostructured thin catalytic layer 125 on it. In some cases, there maybe a residual layer 120 of the material used to form the nanostructuredcatalyst support elements between the carrying substrate 115 and thenanostructured thin catalytic layer 125. The nanostructured thincatalytic layer has a first surface 122 adjacent to the carryingsubstrate and an exposed second surface 128.

Suitable electrocatalyst decals comprising whiskers made from perylenered on a polyimide substrate known as NSTF catalyst layers are availablefrom 3M. Other electrocatalyst decals with nanostructured thin catalyticlayers could also be used. The nanostructured catalytic materials areeither uniformly dispersed on the substrate or dispersed in a desiredpattern. For example, aligned carbon nanotubes, aligned carbonnanofibers, or nanoparticles, and the like with uniformly dispersedcatalyst could be used. Electrocatalyst decals incorporating suchmaterials are described, for example, in Hatanaka et al., PEFCElectrodes Based on Vertically Oriented Carbon Nanotubes, 210^(th) ECSMeeting, Abstract #549 (2006); Sun et al., Ultrafine PlatinumNanoparticles Uniformly Dispersed on Arrayed CN_(x) Nanotubes with HighElectrochemical Activity, Chem. Mater. 2005, 17, 3749-3753; Warren etal., Ordered Mesoporous Materials from Metal Nanoparticle-BlockCopolymer Self-Assembly, Science Vol. 320, 1748-1752 (27 Jun. 2008).

The nanostructured thin catalytic layer on the carrying substrate isinverted, and the second surface 128 of the nanostructured thincatalytic layer 125 is placed in contact with the adhesive layer 110 toform a composite structure. Suitable processes include, but are notlimited to, static pressing with heat and pressure, or for continuousroll production, laminating, nip rolling, or calendering. The carryingsubstrate 115 is then removed (for example, by peeling off the carryingsubstrate). As shown in FIG. 1C, after the carrying substrate isremoved, the residual layer 120 (if present) remains on thenanostructured catalytic layer 125.

The adhesive layer 110 is then removed by a suitable process, as shownin FIG. 1D. One example of a suitable process involves rinsing thecomposite structure with a solvent to dissolve the adhesive. The solventdesirably wets the surface of the porous transfer substrate 105.Suitable solvents include, but are not limited to, water/alcoholmixtures, such as for example, a water/isopropanol (IPA) mixture when anePTFE substrate is used. The alcohol in the water/alcohol mixture helpswet the hydrophobic ePTFE substrate, and the pores of the poroussubstrate act as a drain for the solvent.

The nanostructured thin catalytic layer 125 can be further treated toremove the residual layer 120 (if necessary), exposing the first surface122 of the nanostructured thin catalytic layer 125. The residual layeris typically the left over materials used to form the nanostructuredcatalyst support elements. For example, when the nanostructured thincatalytic layer is a layer of whiskers made from perylene red, theresidual layer is non-crystallized perylene red. For othernanostructured thin catalytic layers, the residual layer would bedifferent. For example, it might be Fe or Ni catalysts used to growcarbon nanofibers or carbon nanotubes.

The residual layer 120 can be removed by any suitable process. Oneexample of a suitable process is rinsing the nanostructured thincatalytic layer with a solvent to remove the residual layer. If thenanostructured thin catalytic layer comprises whiskers made fromperylene red, suitable solvents for perylene red, include, but are notlimited to, mixtures of water, acetone, n-propanol (NPA), or1-methyl-2-pyrolidone (NMP). Water/NPA mixtures can remove small amountsof perylene red (low solubility). NMP appears to be very effective todissolve perylene red, but it has a high boiling point and thus furthersolvent rinsing is required to fully remove it. Consequently, mixturesof the above mentioned solvents are preferred to perform the cleaningprocess. Again, the pores of the porous substrate act as a drain for thesolvent and dissolved residual materials. If Fe or Ni catalysts are usedto grow carbon nanotubes or carbon nanofibers, nitric acid, sulfuricacid, and other acids could be used to dissolve the residual metals.Alcohol could be added to the acidic solution to help wet the ePTFEsubstrate, if desired.

The adhesive layer 110 and residual layer 120 can be removedsimultaneously by applying solvents for both layers at the same time.Alternatively, one layer can be removed after the other. In thissituation, the adhesive layer 110 would preferably be removed first inorder to clear up the path to the pores in the porous transfersubstrate.

Vacuum 132 can be applied when removing the adhesive and/or the residuallayer, if desired.

Alternatively, a nanostructured thin catalytic layer on its originalcarrying substrate can be used as the donor decal.

The acceptor decal can be made as shown in FIGS. 2A-D. Similar to FIG.1, the nanostructured thin catalytic layer is transferred from itscarrying substrate to a transfer substrate. There is a transfersubstrate 205 with an adhesive layer 210, as shown in FIG. 1A. That iscombined with an electrocatalyst electrode decal having a carryingsubstrate 215 and a nanostructured thin catalytic layer 225, and thecarrying substrate 215 is removed, as shown in FIG. 2B. The structureshown in FIG. 2C is left after the removal of the carrying substrate.

The main difference between the donor decal and the acceptor decal isthat the adhesive layer is removed from the donor decal, but it is notremoved from the acceptor decal. The presence of the adhesive layerbetween the substrate and the nanostructured thin catalytic layer in theacceptor decal means that the nanostructured thin catalytic layer ismore securely bonded to the substrate than it is in the donor decal.This ensures that the donor nanostructured thin catalytic layer istransferred to the acceptor decal.

An intermediate layer 230 can be added, if desired. A second adhesivelayer 235 is applied, yielding the structure shown in FIG. 2D. Theadhesive layer is preferably applied to the nanostructured thincatalytic layer of the acceptor decal, and the nanostructured thincatalytic layer of the donor decal preferably does not have adhesive onit. This helps to obtain a clean transfer of the nanostructured thincatalytic layer from the donor decal to the acceptor decal. If theadhesive is applied on the donor decal as shown in FIG. 1, the solventshould be carefully selected so that the adhesive layer only forms ontop of the nano structured thin catalytic layer. If the adhesivepenetrates through the nanostructured thin catalytic layer during thecoating process, the adhesive could bond the nanostructured thincatalytic layer to the donor substrate again. However, the adhesivelayer can be applied to either the nanostructured thin catalytic layerof the acceptor decal, or the donor decal, or both, if desired.

As shown in FIG. 3A, a reconstructed electrode decal with twonanostructured thin catalytic layers can be made by combining the donordecal from FIG. 1D with the acceptor decal of FIG. 2D. The donorsubstrate 105 is then removed. A cleaning solution 237 is then appliedto the structure to remove adhesive layers 210 and 235, as shown in FIG.3B. After removal of the adhesive layers, there is a reconstructedelectrode decal with two nanostructured thin catalytic layers 225, 125separated by intermediate layer 230 on acceptor substrate 205, as shownin FIG. 3C.

The process can be repeated with additional donor decals (having eitherthe same structure or a different structure) to add additionalnanostructured thin catalytic layers to the stack. In this case, theadhesive layers in the acceptor decal would not be removed until all thedesired layers had been transferred to the acceptor decal.

An alternative embodiment of the donor decal is shown in FIGS. 4A-C.FIG. 4A shows a porous substrate 105 pre-coated with an intermediatelayer 130. An adhesive layer 110 is coated over the intermediate layer130. The nanostructured thin catalytic layer 125 is transferred from acarrying substrate and the carrying substrate is removed, leaving thestructure shown in FIG. 4B. The adhesive layer 110 (and the residuallayer on the nanostructured thin catalyst layer, if any) is removed,leaving the structure of FIG. 4C.

Intermediate layer 130 can include adhesive and one or more ofconductive particles, including, but not limited to carbon powder, andcarbon fibers; catalyst; titanium dioxide; silica; nanofibers; ornanotubes. Ionomer could be included in the intermediate layer 130 toadjust the final ionomer content in the intermediate layer. Its usageneeds to be kept to minimum so that ionomer would not block the pores ofthe porous substrate, and make the intermediate layer adhere toostrongly to the porous substrate 105. Desirably, the intermediate layerincludes a removable adhesive and one or more additional materials.

The intermediate layer can be made using the same adhesive as in theadhesive layer used to transfer the nanostructured thin catalytic layerfrom the carrying substrate to the transfer substrate or using adifferent adhesive. If the same adhesive is used in adhesive layer andthe intermediate layer (or if a solvent is used which can remove bothadhesives), the adhesive in the intermediate layer will be removed atthe same time as adhesive layer, leaving ionomer and any additionalmaterials (if present). If a different adhesive it used, another solventcan be used to remove the adhesive in the intermediate layer.

If the adhesive layer contains one or more additional materials, theadditional materials in the intermediate layer can be same as those inthe adhesive layer, or they can be different, if desired.

An alternative embodiment of the acceptor decal is shown in FIGS. 5A-C.FIG. 5A shows a porous substrate 205 pre-coated with an intermediatelayer 230. An adhesive layer 210 is coated over the intermediate layer230. The nanostructured thin catalytic layer 225 is transferred from acarrying substrate and the carrying substrate is removed, leaving thestructure shown in FIG. 5B. An additional intermediate layer 233 isapplied over the nanostructured thin catalytic layer 225. The additionalintermediate layer can generally include the same materials as discussedabove with respect to the intermediate layer. The intermediate layerscan be made of the same materials in the same or different amounts, ordifferent materials, as desired. For example, ionomer can be added toadjust the final ionomer content in the additional intermediate layerfor the final electrode, or the amount and/or type of carbon or catalystcan be adjusted in various intermediate layers.

The thickness of the intermediate layer can be controlled by depositingdifferent amounts of the intermediate layer materials on the substrateor nanostructured thin catalytic layer.

An adhesive layer 235 is applied over the additional intermediate layer230, resulting in the structure of FIG. 5C, which can be used as anacceptor decal.

FIGS. 6A-H illustrate one method of making a reconstructed electrodedecal having three nanostructured thin catalytic layers.

As shown in FIG. 6A, there is an acceptor decal with a porous substrate605A with an intermediate layer 630A, and an adhesive layer 610A (thesame structure as shown in FIG. 5A). A donor decal with a nanostructuredthin catalytic layer 625B is hot pressed adjacent to the adhesive layer610A. The substrate is removed, leaving the structure shown in FIG. 6B.

An intermediate layer 630C and an adhesive layer 610C are then coated onthe stack, as shown in FIG. 6C.

A donor decal having the same structure as shown in FIG. 4C is providedincluding transfer substrate 605D, intermediate layer 630D, andnanostructured thin catalytic layer 625D. The donor decal is bonded tothe stack, as shown in FIG. 6D. The substrate 605D is then removed, asshown in FIG. 6E.

An adhesive layer 610F is then coated on the stack, as shown in FIG. 6F.

A second donor decal having the same structure as FIG. 4C is providedincluding transfer substrate 605G, intermediate layer 630G, andnanostructured thin catalytic layer 625G. The second electrode decal isbonded to the stack, as shown in FIG. 6G. The substrate 605G is thenremoved.

The stack is then treated to remove the adhesive layers, and theadhesive in the intermediate layers (if any), using appropriate methodsas discussed above, such as coating with one of more solvents. Theporous substrate 605A acts as a drain for the wastes. Vacuum ispreferably applied. Optionally, ionomer can be applied at one or moresteps during the process.

The resulting reconstructed electrode decal has three nanostructuredthin catalytic layers separated by intermediate layers, as shown in FIG.6H. There is an acceptor substrate 605A, intermediate layer 630A,nanostructured thin catalytic layer 625B, intermediate layer 630C,nanostructured thin catalytic layer 625D, intermediate layer 630D,nanostructured thin catalytic layer 625G, and intermediate layer 630G.Additional layers, such as an ionomer solution, can be coated on top of630G before MEA fabrication.

When a reconstructed electrode decal with multiple nanostructured thincatalytic layers is made, the arrangement of the first and secondsurfaces of the nanostructured thin catalytic layers will depend on whattype of decals are used to produce it (e.g., electrocatalyst decals oncarrying substrates, or reconstructed electrode decals on transfersubstrates, and how many nanostructured thin catalytic layers areincluded). This is not an important consideration for this type ofstructure, and any suitable arrangement can be used.

It should be noted that the terms donor decal and acceptor decal arerelative terms and depend on whether the structure is donating itsnanostructured thin catalytic layer(s) or accepting a nanostructuredthin catalytic layer(s) from another decal in the particular transferprocess being discussed. For example, after an acceptor decal hasaccepted one or more nanostructured thin catalytic layer(s), thetemporary adhesive in the stack on the acceptor decal can be removed,and it can be used as a donor decal to donate its nanostructured thincatalytic layer(s) to another acceptor decal, as shown above in FIGS. 6Dand 6G once the temporary adhesive is removed.

FIGS. 7A-D show one embodiment of a method of transferring a 3M NSTFcatalyst layer made with perylene red from a polyimide carryingsubstrate to an ePTFE transfer substrate.

FIG. 7A shows an ePTFE porous substrate 705 coated with a water solublePVA (molecular weight around 10,000) adhesive layer 710 through a 5 wt %aqueous solution. The PVA loading is about 6 mg/cm² after drying.

A 3M NSTF catalyst layer supported on a carrying substrate was provided.In this case, the catalyst loading in the nanostructured thin catalystlayer was 0.15 mg Pt/cm². The 3M NSTF catalyst layer included apolyimide carrying substrate, and a nanostructured thin catalytic layerof whiskers made from perylene red 725. There was a residual layer ofperylene red 720 on the interface between the whiskers and the polyimidecarrying substrate. Using a hot press (105° C., 3.5 MPa, 4 minutes)process, the second surface 728 of the layer of whiskers 725 was pressedagainst the PVA adhesive layer 710 on the ePTFE porous transfersubstrate 705. The carrying substrate was then peeled off, leavingwhisker layer 725 on the porous transfer substrate 705 and the residuallayer of perylene red 720 exposed, as shown in FIG. 7B.

As shown in FIG. 7C, the PVA adhesive layer 710 was then removed bycoating a water/IPA (1:1 weight ratio) mixture solution multiple timesuntil the solvent drained freely through the ePTFE substrate. AnEtOH/NPA (1:1) mixture solution was then coated on top of the whiskers725 multiple times to remove the residual layer of perylene red 720,exposing first surface 722.

A diluted DuPont DE2020 ionomer solution (0.2 wt % in NPA:EtOH:H₂O=1:2:2solution) was then coated on top of the whiskers to incorporate theionomer into the whisker matrix. The ionomer solution drains across thewhisker layer and thus coats a thin ionomer film on the surfaces of thewhiskers. Depending on the ionomer concentration and the amount of theionomer solution coated, a layer of ionomer film could be built up ontop of the exposed surface 722 of the whiskers as well, layer 730, asshown in FIG. 7D. Excessive ionomer drained through the pores of theePTFE substrate, and thus no continuous ionomer film would be formed onthe interface 728 between the whiskers 725 and the porous carryingsubstrate 705.

Vacuum 732 was applied during the removal of the adhesive layer, and/orthe removal of the residual materials from the formation of thenanostructured elements, and/or the deposition of the ionomer solution.

An excess amount of ionomer can also be used by increasing the ionomerconcentration or through multiple coating passes, and a thick ionomerfilm would be formed on top the whiskers layer 725. The excessive thickionomer film will help to improve the interface between the whiskers andthe PEM during the final CCM fabrication process, especially when thenanostructured thin catalytic layer carries over the corrugatedstructure from its carrying substrate. The thick ionomer film will beagainst the PEM during the hot press process to fabricate the CCM, andit will become part of the membrane once it is made into MEAs, and thusit would not hurt the fuel cell performance.

FIGS. 8A-B show SEM images of the cross-section of the reconstructeddecal of FIG. 1C. This figure shows that the temporary adhesive PVA 810on the ePTFE substrate 805 deformed itself to fit into the corrugatedstructure of NSTF. The whiskers 825 penetrate into PVA layer 810. Italso shows that the residual backing layer 820 is exposed to the outersurface. The catalyst loading in the nanostructured thin catalyst layerwas 0.15 mg Pt/cm².

FIGS. 9A-D show top down SEM images of a set of whiskers transferred tothe ePTFE substrate at the stage of FIG. 1D at successively highermagnifications after the temporary adhesive PVA is removed. Thesefigures show the clean and nearly complete transfer of the whiskers tothe ePTFE substrate with the whisker backing layer exposed. FIGS. 10A-Bshow SEM images of the cross-section of the whiskers on the ePTFEsubstrate of FIG. 9. The ePTFE porous substrate 905 with the layer ofwhiskers 925, and the exposed first surface can be seen. The SEM imagesof FIGS. 9-10 were taken after the PVA adhesive was removed and beforeany additional layer was deposited. The whiskers stay intact on theePTFE substrate after the removal of the temporary PVA adhesive.

Example 1

An ePTFE porous substrate was coated with a water soluble PVA (molecularweight around 10,000) adhesive layer using a 5 wt % aqueous solution.The PVA loading was about 0.6 mg PT/cm² after drying.

A 3M NSTF catalyst layer supported on a carrying substrate was provided.In this example, the catalyst loading in the nanostructured thincatalyst layer was 0.05 mg Pt/cm². The 3M NSTF catalyst layer included apolyimide carrying substrate, and a nanostructured thin catalytic layerof whiskers made from perylene red. There was a residual layer ofperylene red on the interface between the whiskers and the polyimidecarrying substrate. Using a hot press (105° C., 3.5 MPa, 4 minutes)process, the second surface of the layer of whiskers was pressed againstthe PVA adhesive layer on the ePTFE porous transfer substrate. Thecarrying substrate was then peeled off, leaving whisker layer on theporous transfer substrate and the residual layer of perylene redexposed.

The PVA adhesive layer was removed by coating a water/IPA (1:1 weightratio) mixture solution multiple times until the solvent drained freelythrough the ePTFE substrate. An EtOH/NPA (1:1) mixture solution wascoated on top of the whiskers multiple times to remove the residuallayer of perylene red, exposing the first surface.

A diluted DuPont DE2020 ionomer solution (0.2 wt % in NPA:EtOH:H₂O=1:2:2solution) was then coated on top of the whiskers to incorporate theionomer into the whisker matrix. The ionomer solution drains across thewhisker layer and thus coats a thin ionomer film on the surfaces of thewhiskers.

FIGS. 11A-B show SEM images of the cross section of the whiskers on theePTFE substrate of FIG. 7D. In this case, the catalyst loading in thewhisker catalyst layer was 0.05 mg Pt/cm². The image shows the ePTFEsubstrate 705 with the thin layer of ionomer 730 on the exposed surfaceof the nanostructured whisker catalyst layer 725.

FIG. 12A-B show the cross-section of an CCM made through hot pressing(145° C., 1.4 MPa, 4 minutes) the reconstructed electrode decal shown inFIG. 11 onto a DuPont Nafion® NRE211 membrane. The whiskers have beenattached to the PEM 740 and the ePTFE porous substrate 705 has beenremoved. As it can be seen, the ionomer coated side of the whisker layeris now against the PEM. The thin ionomer film 730 has become part of thePEM 740 and the whiskers 725 are intimately against the PEM 740.

Example 2

Another embodiment of a method of transferring a 3M NSTF catalyst layermade from perylene red on a polyimide carrying substrate to an ePTFEtransfer substrate is shown in FIGS. 13A-D.

FIG. 13A shows an ePTFE porous substrate 1305 is pre-coated with anintermediate layer 1330. Intermediate layer 1330 included a mixture ofPVA and Vulcan XC-72 carbon from Cabot Corporation. The weight ratiobetween PVA and Vulcan carbon was 1:1. The solvent used in this ink wasNPA:EtOH:H₂O=1:2:2.

A PVA adhesive layer 1310 was coated on top of the intermediate layer1330.

A nanostructured thin catalytic layer on a carrying substrate includinga polyimide substrate, a residual layer of perylene red 1320, andwhiskers 1325 was placed in contact with the PVA adhesive layer 1310 toform a composite structure. The polyimide substrate was removed afterhot press. The remaining structure is shown in FIG. 13B.

The PVA adhesive layer 1310 and the PVA adhesive in intermediate layer1330 was then removed with a water/IPA mixture. The whiskers could mixinto the intermediate layer 1330 after the temporary PVA adhesive isremoved.

The residual layer of perylene red 1320 was removed by rinsing thewhiskers 1325 with an EtOH/NPA mixture, exposing first surface 1322, asshown in FIG. 13C.

An ionomer solution diluted from DuPont Nafion® DE2020, 1333 was addedas shown in FIG. 13D by coating the diluted ionomer solution (0.5 wt %with IPA:H₂O=1:1 solution) onto the whiskers. The ionomer solutiondrained through the intermediate layer 1330 and the whisker layer 1325and thus coated a thin ionomer layer film on the particles in theintermediate layer 1330 and on the surface of the whiskers. In thiscase, excessive ionomer was used to build up a thick ionomer layer 1333on top of the whisker layer 1325.

Vacuum 1332 was applied during the removal of the adhesive layer, and/orthe removal of the residual material from the whisker formation, and/orthe deposition of the ionomer layer.

FIGS. 14A-B are SEM images of the cross-section of the reconstructedelectrode made according to Example 2. The ePTFE substrate 1305 has thelayer of Vulcan carbon 1330 sandwiched between the layer of whiskers1325 and ePTFE substrate 1305. The excessive ionomer 1333 built up ontop the whisker layer can be clearly seen. FIGS. 15A-B are SEM images ofthe cross-section of an CCM made through hot pressing (145° C., 1.4 MPa,4 minutes) the electrode decal shown in FIG. 14 onto a DuPont Nafion®NRE211 membrane. The whiskers have been attached to the PEM 1340 and theePTFE porous substrate 1305 has been removed. As it can be seen, theexcessive ionomer film 1333 formed on top of the whisker layer is notvisible any more. It has become part of the PEM 1340, and the whiskers1325 are intimately against the PEM 1340. The carbon layer 1330 is nowexposed and becomes the surface of the catalyst coated membrane.

Example 3

Another embodiment of a method of transferring a NSTF catalyst layerfrom a polyimide carrying substrate to an ePTFE transfer substrate isshown in FIGS. 16A-D. FIG. 16A shows an ePTFE porous substrate 1605coated with a PVA adhesive layer 1610.

The nanostructured thin catalytic layer including a polyimide carryingsubstrate, a perylene red residual layer 1620, and whiskers 1625 withnanostructured thin catalyst Pt loading at 0.05 mg Pt/cm², was contactedwith the PVA adhesive layer 1610 using a hot press process (105° C., 3.5MPa, and 4 minutes) to form a composite structure. The polyimidesubstrate was peeled off after hot pressing, leaving the structure shownin FIG. 16B.

The PVA adhesive layer 1610 was then removed using a water/IPA:solution(1:1 weight ratio), and the perylene red residual layer 1620 was alsoremoved using an EtOH/NPA mixture.

An intermediate layer 1630 containing DuPont Nafion® DE2020 ionomer andPt/Vulcan TEC10V50E catalyst from Tanaka Kikinzoku Kogyo K. K., wasadded as shown in FIG. 16D by coating an ink with the ionomer to Vulcancarbon weight ratio at 1.5 in a solvent of H₂O:EtOH:NPA=2:2:1 onto thewhiskers layer 1625. The Pt loading in the Pt/Vulcan layer 1630 is 0.05mg Pt/cm². When the ink of carbon or catalyst mixed with ionomer iscoated onto the whisker layer 1625, the solution will drain through thewhisker layer 1625 and thus also coat a thin ionomer layer film on thesurface of the whiskers.

Vacuum 1632 was applied during the removal of the adhesive layer, and/orthe removal of the residual perylene red, and/or the deposition of theionomer layer.

FIGS. 17A-B are SEM images of the cross-section of the reconstructedelectrode decal made according to Example 3. The electrode has thewhiskers 1625 between a layer of Pt/Vulcan catalyst mixed with Nafion®DE2020 ionomer 1630 and ePTFE substrate 1605. FIGS. 18A-B are SEM imagesof the cross-section of a catalyst coated membrane made using thereconstructed electrode decal from FIG. 17 through hot pressing (145°C., 1.4 MPa, 4 minutes) onto a DuPont Nafion® NRE211 membrane. Theelectrode has a layer of Pt/Vulcan catalyst mixed with Nafion® DE2020ionomer 1630 between PEM 1640 and the whiskers 1625. After the transfer,the whiskers 1625 are exposed on the CCM.

Example 4

Another embodiment of a method of transferring a nanostructured thincatalytic layer from a polyimide carrying substrate to an ePTFE transfersubstrate is shown in FIGS. 19A-D. FIG. 19A shows an ePTFE poroussubstrate 1905 first coated with an intermediate layer 1930 beforecoating a PVA adhesive layer 1910 on top of intermediate layer 1930.Intermediate layer 1930 is a mixture of PVA adhesive and Vulcan XC-72carbon from Cabot Corporation.

The nanostructured thin catalytic layer including a polyimide substrate,a perylene red residual layer 1920, and whiskers 1925 was contacted withthe PVA adhesive layer 1910 using a hot press process to form acomposite structure (105° C., 3.5 MPa, and 4 minutes). The polyimidesubstrate was removed, leaving the structure shown in FIG. 19B.

The PVA adhesive layer 1910 and the PVA in the intermediate layer 1930was then removed using a water/IPA solution (H₂O:IPA=1:1 weight ratio).The perylene red residual layer 1920 was removed by rinsing the whiskerswith an H₂O/NPA mixture.

An additional intermediate layer 1933 containing DuPont Nafion® DE2020ionomer solution and Vulcan XC-72 carbon from Cabot Corporation wasadded as shown in FIG. 19D by coating an ink with the ionomer to Vulcancarbon weight ratio at 1.5 in a solvent of H₂O:EtOH:NPA=2:2:1 onto thewhiskers matrix 1925.

Vacuum 1932 was applied during the removal of the adhesive layer, and/orthe removal of the residual perylene red, and/or the deposition of theionomer layer.

FIGS. 20A-B show SEM images of the reconstructed electrode containingthe nanostructured thin catalytic layer on the porous ePTFE substrate ofExample 4 with the whiskers 1925 sandwiched between the carbonintermediate layer 1930 and the carbon/ionomer intermediate layer 1933.FIGS. 21A-B show SEM images of catalyst coated membranes made using thereconstructed electrode decal containing the nanostructured thincatalytic layer of Example 4 by hot pressing the finished decal fromFIG. 14 against a DuPont Nafion® NRE211 PEM. On PEM 1940 arecarbon/ionomer intermediate layer 1933, the whiskers 1925, and exposedcarbon intermediate layer 1930.

During the application of the ionomer solution or an ink containingionomer and other particles, the ionomer will drain across the whiskerlayer and the intermediate layer to the pores of the porous substrateand thus coat a thin layer of ionomer on the particles in theintermediate layer and the surfaces of the individual whiskers, whichwould help the proton conduction during fuel cell operation.

Example 5

This example shows the manufacture of an MEA using a reconstructedelectrode decal having two nanostructured thin catalytic layers madeaccording to the general process described in FIGS. 1-3.

FIGS. 22A-D show the preparation of one embodiment of a reconstructedelectrode decal containing two layers of the nanostructured thincatalyst layers. A donor decal as described in FIG. 1, having an NSTFlayer (0.05 mg Pt/cm²) 2225A on a porous ePTFE substrate 2205A, wascompressed against an acceptor decal as described in FIG. 2, having anePTFE porous substrate 2205B, a temporary PVA adhesive layer 2210B, anNSTF layer (0.05 mg Pt/cm²) 2225B, an intermediate layer 2230Bcontaining DuPont Nafion® DE2020 ionomer and Pt/Vulcan TEC10V50Ecatalyst from Tanaka Kikinzoku Kogyo K. K. (0.05 mg Pt/cm²), and anothertemporary PVA adhesive layer 2235B. The whole stack was hot pressed(105° C., 3.5 MPa, and 4 minutes) to form a composite structure, and thesubstrate 2205A from the donor substrate was peeled off.

The PVA adhesive layers, 2210B and 2235B, were removed using a water/IPAsolution (1:1 weight ratio) by coating the solution 2237 multiple timeson top of 2225A as shown in FIG. 22B until the solution drained freely.A reconstructed decal having a Pt/Vulcan catalyst layer 2230B betweentwo NSTF layers 2225B and 2225A on the acceptor substrate 2205B wasformed, as shown in FIG. 22C.

An ionomer solution diluted from DuPont Nafion® DE2020 was added asshown in FIG. 22D by coating the diluted ionomer solution (0.5 wt % withIPA:H₂O=1:1 solution) onto the NSTF layer 2225A. The ionomer solutiondrained through the intermediate layer 2230B and the NSTF layers 2225Aand 2225B and thus coated a thin ionomer layer film on the particles inthe intermediate layer 2230B (not shown) and on the surface of thewhiskers 2238.

FIGS. 23A-B show a reconstructed electrode decal with two nanostructuredthin catalytic layers. There are two nanostructured thin catalytic layer2225A and 2225B separated by a Pt/Vulcan and ionomer mixtureintermediate layer 2230B on the acceptor ePTFE substrate 2205B. FIGS.24A-B show a CCM made by hot pressing the finished decal from FIG. 23against a DuPont Nafion® NRE211 PEM 2240. Nanostructured thin catalyticlayer 2225A is adjacent to the membrane 2240.

The following describes the fabrication method to prepare a catalystcoated diffusion media containing one or more nanostructructed thincatalyst layer(s). The gas diffusion media layer normally containscarbon fiber paper or cloth substrate with a microporous layer (MPL)thereon. Suitable carbon fiber paper or carbon cloth materials areavailable, for example, from Toray Industries, Inc., Mitsubishi RayonInc., Freudenberg Group, and SGL Group. The microporous layer normallycontains carbon powders and hydrophobic fluoropolymers. Because of thelack of inherent adhesive strength in the MPL and adhesion strength tothe carbon fiber substrate, the nanostructured thin catalytic layercannot be directly transferred to the gas diffusion media layer.Consequently, a pretreatment process was developed to maintain theintegrity of the MPL layer and its adhesion to the carbon fibersubstrate so as to enable the transfer of the nanostructured thincatalyst layer. The gas diffusion media layer with a microporous layerthereon is pretreated with a solution containing a temporary adhesive,or ionomer, or a combination of temporary adhesive and ionomer, beforeany transfer. The adhesive solution will seep into the microporous layerand the carbon fiber paper matrix. Once dried, the adhesive will be ableto temporarily increase the inherent adhesion strength within themicroporous layer and to the carbon fiber substrate. The nanostructuredthin catalyst layer can then be transferred to the microporous layerfrom its original carrying substrate to MPL/CFP or the nanostructuredthin catalyst layer donor decal as described above.

The CCDM can include one or more nanostructured thin catalytic layers,optionally with one or more intermediate layers. Depending on how theCCDM is made, either the first or second surface of the nanostructuredthin catalytic layer(s) could be facing the MPL.

FIGS. 25A-B illustrate how the pretreatment of gas diffusion media isperformed. The diffusion media includes carbon fiber substrate 2550 withadjacent microporous layer 2555.

A solution containing a temporary adhesive 2560 is coated on themicroporous layer 2555. The solution can also include some ionomertogether with the adhesive, if desired. The solution wets the MPL sothat the solvent and the soluble temporary adhesive penetrate into themicroporous layer 2555 and optionally also into the carbon fibersubstrate 2550. The temporary adhesive temporarily binds the particlesin the microporous layer together, and also binds the microporous layerto the carbon fiber paper. The temporary adhesive forms a thin bondinglayer on top of the MPL 2555. An additive can be included in thesolution to adjust the solution surface energy in order to help itpenetrate into the microporous layer and carbon paper layer, if desired.

The adhesive solution 2560 can optionally include one or more ofconductive particles, including, but not limited to carbon powder, andcarbon fibers; catalyst; titanium dioxide; silica; nanofibers; andnanotubes and thus form a bonding layer containing the temporaryadhesive layer and the optional material on top of the MPL 2555. Thebonding layer can be made from an ink, if desired. Suitable adhesivesinclude, but are not limited to, PVA, polyethylene oxide, polyacrylate,polyethylene vinyl acetate, and soluble cellulose.

One example of a suitable adhesive solution is composed of PVA dissolvedin a mixture of water and alcohol. The alcohol helps wet the surface ofthe microporous layer, so the PVA temporary adhesive will get into themicroporous layer and carbon fiber substrate when the solvent drainsthrough the MPL and CFP.

The method of transferring a nanostructured thin catalyst layer to thepretreated diffusion media is shown in FIGS. 26A-D. The pretreateddiffusion media including the carbon fiber substrate 2550, microporouslayer 2555, and bonding layer 2560 is shown in FIG. 26A. As shown, thetemporary adhesive in the carbon fiber substrate 2550 and microporouslayer 2555 helps to hold them together.

A nanostructured thin catalyst layer on its original carrying substrateor a donor decal as shown in FIG. 1D including a substrate 2505 and ananostructured thin catalytic layer 2525 is inverted and placed on thepretreated diffusion media as shown in FIG. 26B. The electrode decal anddiffusion media can be combined using a suitable process including, butnot limited to, static pressing with heat and pressure, or forcontinuous roll production, laminating, nip rolling, or calendering.

The substrate 2505 is removed, leaving the structure shown in FIG. 26C.If the CCDM is to include a single nanostructured thin catalytic layer,the adhesive in the bonding layer (or the whole bonding layer if thereare no additional materials) and the adhesive in the MPL and CFP can beremoved at this point using a suitable process. One example of asuitable process involves coating on top of FIG. 26C with a solvent todissolve the adhesive. Suitable solvents include, but are not limitedto, water/alcohol mixtures, such as for example, a water/isopropanol(IPA) mixture. When the solvent drains through the pores of themicroporous layer and carbon fiber substrate, the adhesive in the MPLand CFP would also be removed. A vacuum is preferably applied while theadhesive is removed.

If more than one nanostructured thin catalytic layer will be transferredonto the diffusion media, then the bonding layer and the adhesive in theMPL and CFP are not removed at this point. Optionally, an intermediatelayer 2530 can be deposited on the nanostructured thin catalytic layer2525, as shown in FIG. 26D. The intermediate layer can include atemporary adhesive and one or more of ionomer, conductive particles,including, but not limited to, carbon powder, carbon fibers; catalyst;titanium dioxide; silica; nanofibers; and nanotubes. A bonding layer2535 can also be applied onto the nanostructured thin catalytic layer2525 or the intermediate layer 2530 to increase the adhesion strength ofthe multiple layers on the diffusion media. Additional nanostructuredthin catalyst layers can be transferred by laminating additional donordecals (for example. those shown in FIG. 1D, FIG. 4C or FIG. 6H) againstthe bonding layer 2535.

A vacuum is preferably applied while the solution is coated on thenanostructured thin catalytic layer 2525, and the pores of themicroporous layer and carbon fiber act as a drain.

Example 6

FIG. 27 shows an example of the manufacture of a CCDM with a singlenanostructured thin catalytic layer. The process starts with apretreated diffusion media as shown in FIG. 25, having a carbon fibersubstrate (MRC105 from Mitsubishi Rayon Inc.) 2750 and a microporouslayer 2755 containing a mixture of acetylene back and PTFE which areprecoated with 5 wt % PVA in a water and IPA (3:1) solution. The PVAwill seep into the MPL and carbon fiber substrate when the solution iscoated onto the MPL 2755. A donor decal from FIG. 1, having ananostructured thin catalyst layer NSTF (0.15 mg Pt/cm²) 2725 on aporous ePTFE substrate 2705, was pressed against the bonding layer 2760(105° C., 1.4 MPa, and 4 minutes). The donor substrate 2705 was thenpeeled off to form the composite shown in FIG. 27B.

The PVA bonding layer 2760 and PVA inside of the MPL and CFP was thenremoved using a water/IPA solution (1:1 weight ratio) by coating thesolution 2737 multiple times on top of 2725 as shown in FIG. 27C untilthe solution drained freely. A reconstructed CCDM with a layer of NSTF2725 on the MPL layer 2755 was then formed as shown in FIG. 27D.

An ionomer solution diluted from DuPont Nafion® DE2020, 2733 was addedas shown in FIG. 27E by coating the diluted ionomer solution (0.5 wt %with IPA:H₂O=1:1 solution) onto the NSTF layer 2725. The ionomersolution will drain across the NSTF layer and coat a thin layer ionomerfilm on the whiskers. Additional ionomer film can also be formed on topof the NSTF layer 2725 which would be against the PEM when MEA isfabricated and thus improve the interface between the NSTF and PEM.

FIGS. 28A-B show the single nanostructured thin catalytic layer 2725 onthe microporous layer 2755 and MRC 105 carbon fiber paper 2750. FIGS.29A-B show the SEM images of the MEA prepared by hot pressing thefinished CCDM from FIG. 28 against a DuPont Nafion® NRE211 PEM 2740. TheNSTF layer 2725 is now positioned between MPL 2755 and the PEM 2740.

Alternatively, instead of using an adhesive alone as the bonding layer,the adhesive can be mixed with an ionomer, or an ionomer can be usedalone. In any of these situations, at least one of conductive particles,carbon powder, carbon fibers, catalyst, titanium dioxide, silica,nanofibers, or nanotubes can be included in the bonding layer. If anadhesive is used in the bonding layer, it is removed as discussed above.If the adhesive is used in combination with ionomer and/or othermaterials, the ionomer and/or other materials are not removed with theadhesive, resulting in removal of a portion of the bonding layer,leaving a residual layer of the ionomer and/or other materials on themicroporous layer. If ionomer is used without adhesive (with or withoutother materials), then at least some of the ionomer would have to beremoved from the MPL to clear the gas transport passes for the fuel cellto run. However, ionomer is very difficult to remove, and the use ofionomer without another adhesive is not desirable.

Example 7

In this example, as shown in FIG. 27E, instead of an ionomer solution asin Example 6, an ink composed of Nafion® DE2020 and Pt/Vulcan TEC10V50Ecatalyst from Tanaka Kikinzoku Kogyo K. K 2730 was coated on top of theNSTF layer 2725. The Pt loading in the Pt/Vulcan and ionomer mixturelayer is 0.05 mg Pt/cm². When the solution drains across the NSTF layer,a thin layer ionomer film will be formed on the whiskers.

FIGS. 30A-B show a CCDM with the MRC 105 carbon fiber layer 2750,microporous layer 2755, nanostructured thin catalytic layer 2725, andPt/Vulcan and ionomer mixture layer 2730. FIGS. 31A-B show the SEMimages of the MEA prepared by hot pressing the finished CCDM from FIG.30 against a DuPont Nafion® NRE211 PEM 2740. The NSTF layer 2725 is nowpositioned between MPL 2755 and the Pt/Vulcan intermediate layer 2730.

CCDM having two or more nanostructured thin catalytic layers can be madeusing similar process to that described in FIG. 3. As shown in FIGS.32A-D, starting with composite as FIG. 26D, the bonding layer 2560 andthe adhesive in the MPL and CFP are not removed, an intermediate layer2530 is deposited on the nanostructured thin catalytic layer 2525 andadditional temporary adhesive is coated on top of the intermediate layer2530 to form a new bonding layer 2535. The intermediate layer caninclude a temporary adhesive and one or more of ionomer, conductiveparticles including, but not limited to, carbon powder, carbon fibers;catalyst; titanium dioxide; silica; nanofibers; and nanotubes. The donordecal of FIG. 1D, having the nanostructured thin catalyst layer 2525A onthe porous ePTFE substrate 2505A, was hot pressed against bonding layer2535 (105° C., 1.4 MPa, and 4 minutes) to form a composite structure.The porous substrate 2505A was removed as shown in FIG. 32B, and acleaning solution 2537 was applied to remove the adhesive layer 2535,2560 and adhesives in the intermediate layer 2530, MPL 2555, and CFP2550, leaving the structure shown in FIG. 32C. An ionomer solution iscoated on top of the second nanostructured thin catalytic layer 2525Aforming ionomer layer 2538. When the solution drains across the NSTFlayers and the intermediate layer, a thin layer ionomer film will beformed on the particles in the intermediate layer and whiskers in theNSTF layers. The excess ionomer layer built up on top of NSTF layer2525A will help improve contact between the PEM and the CCDM when it ismade into an MEA.

Example 8

FIG. 33 shows a reconstructed electrode decal made by combining thedonor decal from FIG. 1D and the acceptor decal of FIG. 5C, whichresults in a reconstructed electrode having two nanostructured thincatalytic layers 3325, 3325 and two intermediate layers 3330, 3330, oneof carbon and one of carbon/Pt. After peeling off the porous substrateof the donor decal and removing the temporary adhesive layers bywashing, the reconstructed electrode decal can be used to prepare eithera CCM by compressing against a PEM, or a CCDM by transferring to apretreated diffusion media as shown in FIG. 25.

Discussion of Results

FIG. 34 shows the performance of an MEA made using a nanostructure thinfilm electrode of the prior art made by transferring the 3M NSTFcatalyst directly from the polyimide carrying substrate to the 32 micron3M proton exchange membrane for comparison. The Pt loading of the 3MNSTF catalytic layer was 0.15 mg Pt/cm². FIG. 35 shows the performanceof an MEA made using a nanostructure thin film electrode of the priorart made by transferring the 3M NSTF catalyst directly from the carryingsubstrate to the Nafion® NRE211 proton exchange membrane for comparison.The Pt loading of the 3M NSTF catalytic layer was 0.05 mg Pt/cm². FIG.36 shows the performance of an MEA made using the reconstructedelectrode containing the 3M NSTF catalyst layer on ePTFE decal ofExample 1 which was fabricated with DuPont Nafion® DE2020 ionomer andNafion® NRE211 proton exchange membrane. FIG. 37 shows the performanceof an MEA made using the reconstructed electrode containing the 3M NSTFcatalytic layer (0.05 mg Pt/cm²) on ePTFE decal of Example 3 which wasalso fabricated with DuPont Nafion® DE2020 ionomer and Nafion® NRE211proton exchange membrane. The intermediate layer between the NSTFcatalytic layer and the membrane was 0.05 mg Pt/cm² TKK TEC10V50EPt/Vulcan catalyst mixed with DuPont Nafion® DE2020 ionomer which wasabout 1 micron thick. FIG. 38 shows the performance of an MEA made usingthe reconstructed electrode containing two 3M NSTF catalyst layers (0.05mg Pt/cm² in each layer) on ePTFE decal of Example 5 which was alsofabricated with DuPont Nafion® DE2020 ionomer and Nafion® NRE211 protonexchange membrane. The intermediate layer between the two NSTF catalyticlayers was 0.05 mg Pt/cm² TKK TEC10V50E Pt/Vulcan catalyst mixed withDuPont Nafion® DE2020 ionomer which was about 1 micron thick. As shownin FIG. 34-38, these MEAs were tested at various temperatures with thesame cell inlet relative humidity at all tested temperatures, 100% forthe anode side and 50% for the cathode side.

The reconstructed 3M NSTF electrode of Example 1 showed the same HAD(hydrogen adsorption/desorption) area (greater than or equal to 10 m²/gPt after a break-in protocol) as the prior art MEA made by compressingthe 3M NSTF catalyst layer directly on the proton exchange membrane. Allof the reconstructed electrodes containing the nanostructured thincatalytic layers showed similar HAD areas when the scan was run to 0.6Vand 1.1V versus SHE reference electrode during cyclovoltammetrymeasurements. It indicates that no contaminants were introduced into thereconstructed electrode containing the nanostructure thin catalyticlayer because most of the contaminants would be oxidized at 1.1V ifpresent and that would have resulted in an increased HAD area.

As it can be seen in FIG. 34 and FIG. 35, the performance of theelectrode fabricated with the prior art method was very poor at lowtemperatures, which represents high humidity operating conditions.

For the performance of the reconstructed electrode of Example 1, bycleaning the residual perylene red layer, inverting the whisker layer,and adding some ionomer into the whisker matrix as shown in FIG. 36,there was some performance improvement compared to the electrodefabricated with the prior art as shown in FIG. 35 at the same Pt loading(0.05 mg Pt/cm²).

A significant improvement is demonstrated in FIG. 37 (Example 3)compared to FIG. 34 when a 1 micron thick layer of Pt/Vulcan catalyst(0.05 mg Pt/cm²) mixed with ionomer was added between the 3M NSTFcatalytic layer (0.05 mg Pt/cm²) and the membrane with ionomer added toboth the whisker layer and the Pt/Vulcan catalyst layer. Goodperformance was observed across the entire temperature range, from wetto dry operating conditions. It should be noted that the total Ptloading (NSTF+Pt/Vulcan) of Example 3 is only 0.10 mg Pt/cm², which islower than the prior art MEA in FIG. 34 (0.15 mg Pt/cm²). Furtherimprovement was observed as shown in FIG. 38 (Example 5) for anelectrode containing two layers of NSTF and an intermediate Pt/Vulcanlayer between them across all of the testing temperatures. The total Ptloading (2×NSTF+Pt/Vulcan) of Example 5 is 0.15 mg Pt/cm², which is thesame as the prior art MEA in FIG. 34 (0.15 mg Pt/cm²).

FIG. 39 shows the performance comparison of the two prior art MEAs asshown in FIG. 34 and FIG. 35, Example 1, Example 3, and Example 5 undera dry testing condition. The cell was tested at 80° C., and the Anodeand Cathode inlet RH were kept at 30% and 10%, respectively. FIG. 40compares the performance of the two prior art MEAs as shown in FIG. 34and FIG. 35, Example 1, Example 3, and Example 5 under a wet testingcondition. The cell was also tested at 80° C., but the Anode and Cathodeinlet RH were both kept at 100%.

As it can be seen, Example 5 outperformed the other samples under bothwet and dry testing conditions. Example 3 also showed very goodperformance considering that the total Pt loading is about ⅔ that ofExample 5. The performance of the two prior art MEAs and Example 1 wasmuch lower. The results clearly show the benefits of adding anadditional Pt/C catalyst intermediate layer to increase the waterstorage capacity and thus improve the fuel cell performance with similarand even lower total Pt loading.

FIG. 41 shows the performance of an MEA made using the reconstructedCCDM electrode containing the 3M NSTF catalyst layer (0.15 mg Pt/cm²) ona microporous layer coated MRC 105 gas diffusion media of Example 6which is fabricated with DuPont Nafion® DE2020 ionomer and Nafion®NRE211 proton exchange membrane. FIG. 42 shows the performance of an MEAmade using the reconstructed CCDM electrode containing the 3M NSTFcatalyst layer (0.10 mg Pt/cm²) and an intermediate Pt/C catalyst layer(0.05 mg Pt/cm²) on a microporous layer coated MRC 105 gas diffusionmedia of Example 7 which is fabricated with DuPont Nafion® DE2020ionomer and Nafion® NRE211 proton exchange membrane. The layer betweenthe NSTF catalytic layer and the membrane was 0.05 mg Pt/cm² TKKTEC10V50E Pt/Vulcan catalyst mixed with DuPont Nafion® DE2020 ionomerwhich was about 1 micron thick, which makes the total Pt loading on thiselectrode 0.15 mg Pt/cm² as well. For the performance of thereconstructed CCDM based MEA of Example 6 as shown in FIG. 41, we cansee the improved performance at low temperatures and comparableperformance at high temperatures when compared to the electrodefabricated with the prior art CCM based MEA as shown in FIG. 34 at thesame Pt loading (0.15 mg Pt/cm²).

A significant improvement was demonstrated in FIG. 42 when a 1 micronthick layer of Pt/Vulcan catalyst mixed with ionomer was added betweenthe 3M NSTF catalytic layer and the membrane with ionomer added to boththe whisker layer and the Pt/Vulcan catalyst layer. Good performance wasobserved across the entire temperature range, from wet to dry operatingconditions. It should be noted that performance of CCDM based Example 7is very similar to the performance of CCM based Example 3 and Example 5as shown in FIG. 37 and FIG. 38, respectively. The MEA structure isessentially the same for Example 3 and Example 7 even though they wereprepared via CCM and CCDM method, respectively.

The various embodiments of the processes take advantage of the uniformlydistributed catalyst or distributed in a desirable pattern on thecarrying substrate produced using prior art processes. These embodimentsavoid re-dispersing the nanostructured catalysts. They allow furthercleaning of the catalyst layer (e.g., removing the residual materialsused to produce the nanostructure supports, such as non crystallizedperylene red backing of the 3M NSTF catalyst layer or residual catalystor materials to fabricate the carbon nanotubes or nanofibers).Additional components or layers can be added into the nanostructuredthin catalytic layer by coating on the stripped nanostructured thincatalyst layer on the porous transfer substrate or pre-coating theporous transfer substrate with a mixture of particles and adhesive.Since all of the processes are carried out on the porous transfersubstrate, this invention is well suited for a continuous process andmass production.

It is noted that terms like “preferably,” “commonly,” and “typically”are not utilized herein to limit the scope of the claimed invention orto imply that certain features are critical, essential, or evenimportant to the structure or function of the claimed invention. Rather,these terms are merely intended to highlight alternative or additionalfeatures that may or may not be utilized in a particular embodiment ofthe present invention.

For the purposes of describing and defining the present invention it isnoted that the term “device” is utilized herein to represent acombination of components and individual components, regardless ofwhether the components are combined with other components. For example,a “device” according to the present invention may comprise anelectrochemical conversion assembly or fuel cell, a vehicleincorporating an electrochemical conversion assembly according to thepresent invention, etc.

For the purposes of describing and defining the present invention it isnoted that the term “substantially” is utilized herein to represent theinherent degree of uncertainty that may be attributed to anyquantitative comparison, value, measurement, or other representation.The term “substantially” is also utilized herein to represent the degreeby which a quantitative representation may vary from a stated referencewithout resulting in a change in the basic function of the subjectmatter at issue.

Having described the invention in detail and by reference to specificembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims. More specifically, althoughsome aspects of the present invention are identified herein as preferredor particularly advantageous, it is contemplated that the presentinvention is not necessarily limited to these preferred aspects of theinvention.

What is claimed is:
 1. A method of making a reconstructed electrodedecal having a plurality of nanostructured thin catalytic layerscomprising: providing an acceptor decal comprising a carrying substratehaving a first nanostructured thin catalytic layer thereon, the firstnanostructured thin catalytic layer having a first surface and a secondsurface, the first surface of the first nanostructured thin catalyticlayer adjacent to the carrying substrate; providing an acceptorsubstrate comprising a porous transfer substrate with an adjacent afirst adhesive layer; adhering the second surface of the firstnanostructured thin catalytic layer adjacent to the first adhesive layerof the acceptor substrate; removing the carrying substrate from thefirst surface of the first nanostructured thin catalytic layer such thatthe first surface of the first nanostructured thin catalytic layerbecomes exposed; applying a second adhesive layer to the first surfaceof the first nanostructured thin catalytic layer; and providing a firstdonor decal comprising a donor substrate with a second nanostructuredthin catalytic layer having an exposed first surface thereon; bondingthe first surface of the second nanostructured thin catalytic layer ofthe donor decal adjacent to the second adhesive layer of the firstnanostructured thin catalytic layer of the acceptor decal; removing thedonor substrate; and removing the first adhesive layer and the secondadhesive layer to form the reconstructed electrode decal comprising theporous transfer substrate, the first nanostructured thin catalytic layeradjacent to the porous transfer substrate, and the second nanostructuredthin catalytic layer adjacent to the first nanostructured thin catalyticlayer on a side opposite the porous transfer substrate.
 2. The method ofclaim 1 further comprising coating a solution onto the secondnanostructured thin catalytic layer after the donor substrate, the firstadhesive layer and the second adhesive layer have been removed, thesolution forming a layer on top of the second nanostructured thincatalytic layer.
 3. The method of claim 2 wherein the solution includesat least one of an ionomer, conductive particles, carbon powder, carbonfibers, catalyst, titanium dioxide, silica, nanofibers, or nanotubes. 4.The method of claim 1 wherein the reconstructed electrode decal havingthe plurality of nanostructured thin catalytic layers further comprisesat least one intermediate layer comprising at least one of an ionomer,conductive particles, carbon powder, carbon fibers, catalyst, titaniumdioxide, silica, nanofibers, and nanotubes, the at least oneintermediate layer being positioned between the acceptor substrate andthe first nanostructured thin catalytic layer or between the firstnanostructured thin catalytic layer and second nanostructured thincatalytic layer.
 5. The method of claim 1 wherein the secondnanostructured thin catalytic layer is bonded adjacent to the firstnanostructured thin catalytic layer using a hot press process.
 6. Themethod of claim 1 wherein there is a residual layer on the firstnanostructured thin catalytic layer, the second nanostructured thincatalytic layer, or both, and further comprising removing the residuallayer.
 7. The method of claim 1 further comprising applying a vacuumwhile removing the first adhesive layer and the second adhesive layer.8. The method of claim 1 wherein the first adhesive layer and the secondadhesive layer comprises a water soluble adhesive.
 9. The method ofclaim 1 wherein a catalyst loading of the first nanostructured thincatalytic layer is different from a catalyst loading of the secondnanostructured thin catalytic layer.
 10. The method of claim 1 whereinthe first adhesive layer and the second adhesive layer further comprisesat least one of ionomer, conductive particles, carbon powder, carbonfiber, catalyst, titanium dioxide, silica, nanofibers, and nanotubes.11. The method of claim 1 wherein providing the first donor decalcomprises: providing an electrocatalyst decal comprising a carryingsubstrate having the second nanostructured thin catalytic layer thereon,the second nanostructured thin catalytic layer having a first surfaceand a second surface, the first surface of the second nanostructuredthin catalytic layer adjacent to the carrying substrate; providing saiddonor substrate comprising a porous transfer substrate with an adjacentadhesive layer; adhering the second surface of the second nanostructuredthin catalytic layer adjacent to the adhesive layer of the poroustransfer substrate to form a composite structure; removing the carryingsubstrate from the composite structure such that a residual layer formedon the first surface of the second nanostructured thin catalytic layerof the electrocatalyst decal becomes exposed; and removing the adjacentadhesive layer from the composite structure and further removing theresidual layer from the composite structure to form the first donordecal, wherein the second surface of the second nanostructured thincatalytic layer is adjacent to the donor substrate.
 12. The method ofclaim 11 wherein the adjacent adhesive layer further comprises at leastone of ionomer, conductive particles, carbon powder, carbon fiber,catalyst, titanium dioxide, silica, nanofibers, and nanotubes.
 13. Themethod of claim 1 further comprising: providing a second donor decalcomprising a second donor substrate with a third nanostructured thincatalytic layer, the third nanostructured thin catalytic layer having afirst surface and a second surface, the second surface of the thirdnanostructured thin catalytic layer adjacent to the second donorsubstrate; applying a third adhesive layer adjacent to the secondnanostructured thin catalytic layer prior to removing the first adhesivelayer and the second adhesive layer; bonding the first surface of thethird nanostructured thin catalytic layer adjacent to the secondnanostructured thin catalytic layer with the third adhesive layer;removing the second donor substrate; and removing the first adhesivelayer, the second adhesive layer and the third adhesive layer to formthe reconstructed electrode decal comprising the porous transfersubstrate, the first nanostructured thin catalytic layer adjacent to theporous transfer substrate, the third nanostructured thin catalytic layeradjacent to the second nanostructured thin catalytic layer and on a sideopposite the porous transfer substrate.
 14. The method of claim 1wherein the acceptor substrate is a porous diffusion media comprising agas diffusion media layer with an adjacent microporous layer.